Radiation therapy release of tumor specific antigen in serum of metastasizing and non-metastasizing experimental rat tumors and its effect on cell-mediated cytotoxicity of lymphocytes and macrophages on syngeneic tumor cells in vitro. Increasing favorable host immune response to metastasizing and non-metastasizing tumors in rats by means of non-specific immune adjuvants C. parvum or BCG prior to radiation therapy. Determined by extent of tumor regression, regrowth, and resistance to rechallenge with graded doses of tumor cells. Enhancement of tumor target cell killing by means of added cytophilic factors in the cell mediated cytotoxicity assay with immune lymphocytes. Explanation for lack of tumor target cell killing in vitro by immune thoracic duct lymphocytes of rats. Determination of effect of lymphoid irradiation upon cytotoxic activity. Enhancement of cytotoxic activity by added non-immune macrophages.